IR absorption spectroscopy

Reflection-Absorption IR spectroscopy (RAIRS) where the linearly polarized IR beam is specularly reflected from the front face of a highly reflective sample, such as a metal single crystal surface (Figure 3.1(a)). This is also sometimes referred to as IRAS (IR reflection absorption). The IR beam comes in at grazing angle (i.e. almost parallel to the surface), and although absorption bands in RAIRS have intensities that are some two orders of magnitude weaker than in transmission studies on... 

For IR measurements, the zeolite powders were pressed into self supporting wafers which were activated by heating in He flow (20 ml/min) up to 773 K with a rate of 10 K/min. During all treatments, the samples were analyzed in situ by means of transmission absorption IR spectroscopy using a Bruker IFS88 FTIR spectrometer The IR cell was constructed as continuously stirred tank reactor (volume=l. 5 cmJ) equipped with 1/16" gas in- and outlet... 

The experimental apparatus, as shown in Figure 11-1, was a standard molecular beam machine with a heated pulsed valve for vaporization of the non-volatile species and for supersonic cooling. Samples of 1-methyluracil, 1,3-dimethyluracil and thymine were purchased from Aldrich Co. and used without further purification. The sample 1,3-dimethylthymine was synthesized from thymine following a literature procedure [33], and its purity was checked by nuclear magnetic resonance (NMR) and infrared absorption (IR) spectroscopy. The heating temperatures varied for different samples 130°C for DMU, 150°C for MU, 180°C for DMT, and 220°C for thymine. No indication of thermal decomposition was observed at these... 

The fundamentals of transmission/absorption IR spectroscopy were developed in the last decades of the nineteenth century and in the very first years of the twentieth century [1], and, as a consequence, IR spectroscopy rapidly became one of the most widely used techniques for chemical analysis. 

IR spectroscopy was mainly used to characterize the sorbed species. The zeolite powder was pressed into self supporting wafers and analyzed in situ during all treatments (i.e., activation, sorption, reaction) by means of transmission absorption IR spectroscopy using a BRUKER IPS 88 FTIR spectrometer (resolution 4 cm" ). For the sorption experiments, an IR cell equipped with IR transparent windows which could be evacuated to pressures below 10" mbar was used [11]. The activated zeolite wafer was contacted with a constant partial pressure (0.001 mbar) of the adsorbate at 308 K until adsorption-desorption equilibrium was reached (which was monitored by time resolved IR spectroscopy). For the coadsorption experiments, the catalysts were equilibrated with 0.001 mbar of both adsorbates admitted in sequentional order. The spectra were normalized for the sample thickness by comparing the intensities of the absorption bands of the adsorbate with the integral intensity of the lattice vibration bands of the zeolite between 2090 and 1740 cm". The surface coverage was quantified by calibration with gravimetric measurements (under conditions identical to the IR spectroscopic experiments). 

Hayden, B.E., King, A. and Newton, M.A. (1999) Fourier transform reflection absorption IR spectroscopy study of formate adsorption on TiO2(110). 

Teraoka, R., Otsuka, M., and Matsuda, Y., 1999, Evaluation of photostability of solid state dimethyl l,4-dihydro-2,6-dimethyl-4-(2-nitrophenyl)-3,5-dicarboxylate by using Fourier-transform reflection-absorption IR spectroscopy, Int. J. Pharm. 184, 35-43. 

Electronic (UV and visible) spectroscopy has not been utilized in a routine manner, most likely due to the fact that the nature of heterocycles is rather difficult to correlate correctly with the chromophoric absorption IR spectroscopy, however, has been applied almost routinely, as this technique can establish unequivocally the presence of various functionalities. 

Energy levels involved in (a) resonant absorption (IR spectroscopy), (b) Raman scattering and (c) single-levei fluorescence. 

Because IR absorption measurements discussed in this book are all performed in optically extremely dilute samples, such as those occurring in molecular beams or tandem mass spectrometers, action spectroscopy is employed instead of direct absorption IR spectroscopy. In conventional direct absorption IR spectroscopy, the attenuation of the light beam transmitted through the sample is measured as a function of the frequency of the IR radiation. By measuring the IR laser beam intensity before and after the sample, the absorbance as a function of the frequency of the IR photons is obtained according to the Lambert-Beer law ... 

Self-supporting pressed discs of the pure oxide powders are prepared for in situ characterisation studies by transmission/absorption IR spectroscopy. These samples are put onto the IR beam, in an appropriate cell allowing heating, cooling, and gas/vapour manipulation. Activation is mostly performed by outgassing at relatively high temperatures. In the case of diffuse reflectance infrared Fourier transform (DRIFT) experiments the pure catalyst powder is deposited on the sample holder, with smooth pressure, and activation is mostly performed by an inert, dry gas flow. 

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